Bug Tracker

Ticket #1818: jQueryBug.html
File jQueryBug.html, 4.2 KB (added by BryceLohr, October 18, 2007 02:20PM UTC)

Demonstrates incorrect width() results

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html lang="en">
<head>
    <title>jQuery width() Bug</title>
    <style type="text/css">
        #div1 {
            position: absolute;
            border: 1px dashed black;
            padding: 10px;
        }
        #div2 {
            position: absolute;
            border: 1px dashed black;
            padding: 10px;
        }
        #div3 {
            width: 200px;
            position: absolute;
            border: 1px dashed black;
            padding: 10px;
        }
        #div4 {
            width: 200px;
            position: absolute;
            border: 1px dashed black;
            padding: 10px;
        }
    </style>
    <script type="text/javascript" src="js/jquery-nightly.js"></script>
    <script type="text/javascript">
        $(function() {
            $("#div2").hide();
            $("#div1w").text( $("#div1").width() );
            $("#div2w").text( $("#div2").width() );

            $("#showBtn").click(function(evt) {
                $("#div1").toggle(); // get div1 out of the way
                $("#div2").toggle();
                $("#div2w").text( $("#div2").width() );
            });

            $("#div4").hide();
            $("#div3w").text( $("#div3").width() );
            $("#div4w").text( $("#div4").width() );

            $("#showBtn2").click(function(evt) {
                $("#div3").toggle(); // get div3 out of the way
                $("#div4").toggle();
                $("#div4w").text( $("#div4").width() );
            });
        });
    </script>
</head>

<body>
    <h1>width() Bug</h1>
    <p>jQuery's width() method returns an incorrect value when used on an invisible element with 
    absolute or fixed positioning. However, this is only the case when the invisible element does 
    not have an explicitly assigned width. This can be traced to the css() method: in its "width" 
    case for invisible elements, it clones the node and sets the padding/border widths to zero to 
    measure the element. The problem is that it also explicitly sets the "left" and "right" edge 
    positions, which will implicitly change the element's width when it has no explicit width. That 
    code appears to be intended to position the element at the origin point of the page, but due to 
    a simple oversight actually ends up changing the element size. This behaviour is consistently 
    incorrect on Firefox 2, IE 7, and Opera 9 (all on Windows; I don't have access to a Mac).</p>

    <p>The work-around, is of course, to display the element before trying to get its size. However, 
    you shouldn't have to do this, and usually you want to position the element before displaying 
    it. Changing the positioning to something else is no good, since that completely changes how
    the browser sizes the element.</p>

    <p>This demonstrates the bug. Watch the #div2/#div4 width values as you click the buttons.</p>


    <h2>Div's without explicit widths</h2>
    <table>
        <tr><th>Div id</th><th>Result of width()</th></tr>
        <tr><td>div1</td><td id="div1w"></td></tr>
        <tr><td>div2</td><td id="div2w"></td></tr>
    </table>

    <input type="button" id="showBtn" value="Toggle #div2">

    <div id="div1">
        This is div #div1
    </div>
    <div id="div2">
        Div #div2 lies here
    </div>


    <h2 style="margin-top: 3em">Div's with explicit widths</h2>
    <table>
        <tr><th>Div id</th><th>Result of width()</th></tr>
        <tr><td>div3</td><td id="div3w"></td></tr>
        <tr><td>div4</td><td id="div4w"></td></tr>
    </table>

    <input type="button" id="showBtn2" value="Toggle #div4">

    <div id="div3">
        This is div #div3
    </div>
    <div id="div4">
        Div #div4 lies here
    </div>


    <h2 style="margin-top: 3em">The Fix</h2>
    <p>The bug has an easy, one-line fix:</p>

    <strong>From: <a href="http://dev.jquery.com/browser/trunk/jquery/src/core.js?rev=3669#L773">src/core.js@3669, line 773</a></strong>
    <pre>right: "0",</pre>

    <strong>To:</strong>
    <pre>top: "0",</pre>
</body>
</html>

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